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AMERICAN SOCIETY OF CIVIL ENGINEERS

INSTITUTED 1852


TRANSACTIONS

Paper No. 1176


REINFORCED CONCRETE PIER CONSTRUCTION.

BY EUGENE KLAPP, M. AM. SOC. C. E.

WITH DISCUSSION BY MESSRS. WILLIAM ARTHUR PAYNE, AND EUGENE KLAPP.




A private yacht pier, built near Glen Cove, Long Island, has brought out
a few points which may be of interest. It is an example of a small
engineering structure, which, though of no great moment in itself,
illustrates the adoption of means to an end that may be capable of very
great extension.

The problem, as submitted to the writer, was to construct a yacht
landing at East Island, on the exposed south shore of Long Island Sound,
in connection with the construction at that point of an elaborate
country residence. The slope of the beach at this point is very gradual,
and it was specified that there should be a depth of at least 4 ft. of
water at low tide. Soundings indicated that this necessitated a pier 300
ft. long. It was further specified that the pier should be to some
extent in keeping with the scale of the place being created there, and
that a wooden pile structure would not be acceptable. Besides these
esthetic conditions, wooden piles were rejected because the teredo, in
this part of the Sound, is very active. At the same time, the owner did
not care to incur the expense of a masonry pier of the size involved.
Also, it was desired to unload on the pier all material for the house
and grounds during construction, and coal and other supplies thereafter,
thus necessitating a pier wide enough to allow access for a cart and
horse and to provide room for turning at the pier head.

[Illustration: PLATE XXX.--YACHT PIER NEAR GLEN COVE, N. Y.]

Comparative designs and estimates were prepared for (_a_) a pier of
ordinary construction, but with creosoted piles; (_b_) a concrete pier
on concrete piles; and (_c_) for a series of concrete piers with wooden
bridge connections. The latter plan was very much the best in
appearance, and the calculated cost was less than that of the pier of
concrete piles, and only slightly more than that of creosoted piles, the
latter being only of a temporary nature in any case, as it has been
found that the protection afforded by creosote against the teredo is not
permanent.

At this point on the Sound the mean range of the tide is about 8 ft.,
and it was determined that at least 5 ft. above mean high water would be
required to make the underside of the dock safe from wave action. There
is a northeast exposure, with a long reach across the Sound, and the
seas at times become quite heavy. These considerations, together with 4
ft. of water at low tide and from 2 to 3 ft. of toe-hold in the beach,
required the outer caissons to be at least 20 ft. high.

To construct such piers in the ordinary manner behind coffer-dams, and
in such an exposed location, was to involve expenditure far beyond that
which the owner cared to incur. The writer's attention had shortly
before been called to the successful use of reinforced concrete caissons
on the Great Lakes for breakwater construction, by Major W. V. Judson,
M. Am. Soc. C. E., and under patents held by that officer. It seemed
that here was a solution of the problem. These caissons are constructed
on the shore, preferably immediately adjoining the work. After thorough
inspection and seasoning, they are usually launched in a manner somewhat
similar to a boat, are towed into position, sunk in place, and then
filled with rip-rap.

In this case what was needed was a structure that could be constructed
safely and cheaply in the air, could then be allowed to harden
thoroughly, and could finally be placed in accurate position. The
weights to be supported were not great, the beach was good gravel and
sand, fairly level, and, under favorable circumstances of good weather,
the placing of the caissons promised to be a simple matter. Therefore,
detailed plans were prepared for this structure.

An effort was made to preserve some element of the yachting idea in the
design, and bow-string trusses, being merely enlarged gang planks, were
used to connect the caissons.

The pier was originally laid out as a letter "L," with a main leg of
300 ft. and a short leg of 36 ft. The pier head consisted of eight
caissons in close contact, and was intended to form a breakwater, in the
angle of which, and protected from the wave action, was to be moored the
float and boat landing. After the first bids were received, the owner
wished to reduce the cost, and every other caisson in the pier head was
omitted, so that, as built, the pier contains eight caissons and five
53-ft. trusses. The caissons supporting the trusses are 8 ft. wide and
12 ft. long, and those in the pier head are 12 by 12 ft. On account of
the shoal water and the great height of the outer caissons in comparison
with their cross-section, it seemed advisable to mould them in two
sections. The reinforcement in the side walls consisted of round 1/2-in.
rods horizontally, and 3/8-in. rods vertically, spaced as shown on Fig.
1, together with cross-diaphragms as indicated.

The caissons were reinforced for exterior pressures, which were to be
expected during the launching and towing into position, and also for
interior pressures, which were to be expected at low tide, when the
water pressure would be nothing, but the filling of the caissons would
be effective. The corners were reinforced and enlarged. In order to
secure a proper bedding into the sand foundation, a 12-in. lip was
allowed to project all around the caisson below the bottom. In the
bottom there was cast a 3-in. hole, and this was closed by a plug while
the lower section was being towed into place.

The question of the effect of sea water on the concrete was given much
thought. The writer is unable to find any authoritative opinions on this
subject which are not directly controverted by equally authoritative
opinions of a diametrically opposite nature. He thinks it is a question
that this Society might well undertake to investigate promptly and
thoroughly. There can be no question that there are many distressing
instances of failures due to the action of sea water and frost on
concrete, and that many able and experienced engineers in charge of the
engineering departments of the great transportation companies have
simply crossed concrete off their list of available materials when it
comes to marine construction. It is a subject too large in itself to be
discussed as subsidiary to a minor structure like the one herein
described, and though many have rejected concrete under these
conditions, other engineers equally conservative are using it freely and
without fear.

The writer consulted with his partner and others at some length, and,
considering all the advantages to accrue by the use of these concrete
caissons, decided to do so after taking all known precautions.

[Illustration: FIG. 1.]

These precautions consisted in:

First, the use of cement in which the chemical constituents were limited
as follows:

It was specified that the cement should not contain more than 1.75% of
anhydrous sulphuric acid (SO_{3}) nor more than 3% of magnesia (MgO);
also that no addition greater than 3% should have been made to the
ingredients making up the cement subsequent to calcination.

Secondly, to secure by careful inspection the most completely
homogeneous mixture possible, with especial care in the density of the
outer skin of the caissons.

Thirdly, a prolonged seasoning process before the new concrete should be
immersed in the sea water.

In addition to these well-known precautions, it was decided to try the
addition to the cement of a chemical element that should make with the
free lime in the cement a more stable and indissoluble chemical
combination than is offered by the ordinary form of Portland cement.
This was furnished by the patent compound known as "Toxement," which is
claimed by the inventor to be a resinate of calcium and silicate of
alumina, which generates a resinate of lime and a silicate of alumina in
crystalline form. It is further claimed that each of these materials is
insoluble in sodium chloride and sodium sulphate, 3% solution. It was
used in all the caissons, excepting Nos. 1 and 2, in the proportions of
2 lb. of Toxement to each 100 lb. of cement. The first two caissons were
not thus treated, and will be held under close observation and
comparison with the others, which were treated with this compound.

The mixture used was one of cement (Pennsylvania brand), two of sand,
and four of gravel. The sand and gravel were from the nearby Cow Bay
supply, and screened and washed. None of the gravel was larger than 1/2
in., grading down from that to very coarse sand. The sand was also
run-of-bank, and very well graded.

The caissons, after being placed, were filled with sand and gravel from
the adjoining beach up to about mean high-water mark, and the edges
outside all around were protected from tidal and wave scour by rip-rap
of "one man" stone.

The trusses were constructed on a radius of 34 ft., with 8 by 8-in.
chords, 6 by 6-in. posts, and 1-in. rods. The loading was figured as a
loaded coal cart plus 100 lb. per ft. All lumber was clear yellow pine,
except the floor, which was clear white oak. The pipe rail and all bolts
below the roadway level, and thus subject to frequent wettings by salt
water, were of galvanized iron. The trusses were set 9 ft. 9 in. apart
on centers, giving a clear opening of 8 ft. between the wheel guards
under the hand-rails. The fender piles were creosoted. The float was 18
ft. long and 12 ft. wide.

A contract was let to the Snare and Triest Company, and work was
commenced early in August, 1909. The first caisson was poured early in
September, and the last about the beginning of October.

The caissons were all cast standing on parallel skids at about mean high
water. It was first intended to construct a small marine railroad and
launch the caissons in that manner, rolling them along the skids to the
head of the marine railway. This plan was abandoned, however, and by
sending in at high tide a powerful derrick scow, many of the caissons
were lifted bodily from their position and set down in the water, towed
to place and sunk in position, while the others, mostly the upper
sections, were lifted to the deck of the scow and placed directly from
there in their final position. There was not much difficulty in getting
them to settle down to a proper bearing. Provision had been made for
jetting, if necessary, but it was not used. In setting Caisson No. 2 a
nest of boulders was encountered, and a diver was employed to clear away
and level up the foundation. The spacing was accomplished by a float
consisting of two 12 by 12-in. timbers, latticed apart, and of just
sufficient length to cover the clear distance between the caissons. The
first caissons being properly set inshore, the float was sent out, guyed
back to the shore, and brought up against the outer edge of the set
caisson. The next caisson was then towed out, set against the floating
spacer, and sunk in position. There was some little trouble in plumbing
the caissons, but, by excavating with an orange-peel bucket close to the
high side and depositing the material against the low side, they were
all readily brought to a sufficiently vertical and level position to be
unnoticed by sighting along the edge from the shore.

The trusses were all constructed in the contractor's yard at Bridgeport,
and were towed across the Sound on a scow. They were set up and braced
temporarily by the derrick boat, and then the floor and deck were
constructed in place.

On December 26th, 1909, a storm of unusual violence--unequaled in fact
for many years--swept over the Sound from the northeast; the waves beat
over the pier and broke loose some floor planks which had been only
tacked in position, but otherwise did no damage, and did not shift the
caissons in the least. The same storm partly destroyed a pier of
substantial construction less than a mile from the one in question.

Unfortunately, the work was let so late in the summer, and the
restrictions as to seasoning the concrete were enforced so rigidly, that
the work of setting the caissons could not be commenced until November
11th, thus the entire construction was forced into the very bad weather
of the late fall and early winter. As this involved very rough water and
much snow and wind, the work was greatly delayed, and was not completed
until the middle of January. The cost of the entire dock was about
$14,000.

The writer believes that the cost was much less than for masonry piers
by any other method of construction, under the existing circumstances of
wind, tide, and exposure.

It would seem that for many highway bridges of short span, causeways,
and similar structures, the use of similar caissons would prove
economical and permanent, and that they might be used very largely to
the exclusion of cribwork, which, after a decade or so, becomes a source
of constant maintenance charges, besides never presenting an attractive
appearance. Finally, in bridges requiring the most rigid foundations,
these caissons might readily be used as substitutes for open wooden
caissons, sunk on a prepared foundation of whatever nature, and still be
capable of incorporation into the finished structure.




DISCUSSION


WILLIAM ARTHUR PAYNE, M. AM. SOC. C. E. (by letter).--On the arrival of
the first barge load of brick, to be used in building a residence on the
estate to which this pier belongs, a severe northwest wind blew for two
days, after the boat was moored alongside, directly against the head of
the pier and the side of the boat. The effect on the pier was to crush
the fender piles and cause a settlement of one of the caissons at the
pier head on the west end. The caisson was knocked slightly out of
alignment, and a settlement toward the west was observable.

The writer believes that this was caused by the pounding of the brick
barge on the sand bottom on which the caissons rest, during half tide,
the boat being raised from the bottom on a roller, and striking when the
roller had passed. In order to protect the pier and avoid the bumping of
barges against it, three groups of piles were driven about 8 ft. beyond
the end, a secondary platform was built between these and the stringer
of the pier, and arranged so that it would slide on the stringer in case
of movement of the piles. This secondary platform is particularly
advantageous in the handling of material, as the height of the dock was
found to be excessive for passing up brick and cement. For handling
material after it is deposited on the dock, an industrial railroad has
been built. At the shore end of this railroad, brick and cement are
dumped into wagons, in which they are carried up the hill to the house.


EUGENE KLAPP, M. AM. SOC. C. E. (by letter).--The injury done to the
piers, as reported by Mr. Payne, is not to be wondered at. The pier was
primarily built for a yacht landing, and, on account of the shoal water
conditions, excepting at extreme high tide, it was mostly to be used by
tenders and launches from larger yachts. It was thought that at high
water the large steam yachts might be able to come alongside.

Provision was not made for tying up to the dock a heavily loaded brick
scow and allowing it to remain there through rough weather.

The building of the secondary fender piles, during the temporary use of
the dock for unloading building material, will doubtless prevent further
damage.